1. Field of the Invention
The invention relates to a liquid crystal compound, a liquid crystal composition and a liquid crystal display device. More specifically, it relates to a 2,3-difluorobenzene derivative having a butene-bonding group, a liquid crystal composition including this compound and having a nematic phase, and a liquid crystal display device containing this composition.
2. Related Art
A liquid crystal display device typified by a liquid crystal display panel, a liquid crystal display module and so forth utilizes optical anisotropy, dielectric anisotropy and so forth, which are possessed by a liquid crystal compound. A variety of operating modes of this liquid crystal display device are known, such as a PC (phase change) mode, a TN (twisted nematic) mode, a STN (super twisted nematic) mode, a BTN (bistable twisted nematic) mode, an ECB (electrically controlled birefringence) mode, an OCB (optically compensated bend) mode, an IPS (in-plane switching) mode, a VA (vertical alignment) mode, a PSA (polymer sustained alignment) mode.
In the operating modes, the ECB mode, the IPS mode, the VA mode and so forth utilize homeotropic orientation of liquid crystal molecules, and it is known that in particular the IPS mode and the VA mode are able to improve a limited viewing angle that is a disadvantage of a conventional display mode such as the TN mode or the STN mode.
A variety of liquid crystal compounds in which hydrogen on the benzene ring had been replaced by fluorine have conventionally been studied as a component of a liquid crystal composition having negative dielectric anisotropy, which can be used for liquid crystal display devices having these operating modes.
For example, the compound (A), in which hydrogen on the benzene ring had been replaced by fluorine, has been studied (see Patent document No. 1). However, the compound has a small optical anisotropy. The compound (B) having alkenyl, in which hydrogen on the benzene ring had been replaced by fluorine, has been studied (see Patent document No. 2). However, the compound does not have a sufficiently large optical anisotropy.
The three-ring compound (C) having an ether-bonding group has been reported (see Patent document No. 3 and Non-patent document No. 1). The compound has a narrow temperature range of a liquid crystal phase (mesophase range), and a liquid crystal composition including the compound has a low maximum temperature of a nematic phase.
The four-ring compound (D) having an ethylene-bonding group has been reported (see Patent document No. 4). However, the compound does not have a sufficiently large negative dielectric anisotropy, and a liquid crystal composition including the compound has a low maximum temperature.
The four-ring compound (E) having an ether-bonding group and an ethylene-bonding group has been reported (see Patent document No. 5). However, a liquid crystal composition including the compound has a low maximum temperature.
The three-ring compound (F) having a butene-bonding group and an ester-bonding group has been reported (see Patent document No. 6). However, the compound does not have a sufficiently large negative dielectric anisotropy and has a large viscosity, and a liquid crystal composition including the compound has a low maximum temperature.
